Monday, July 14, 2008

One issue I've always had with satellite TV is that before recently, every tuner has required so-called "home run" wiring. That is, a coax run all the way from the receiver to either the dish or a multiplexer, with no splitters in-between. The reason for this is that there needs to be a communication path from the tuner back to the dish (or multiplexer) so that it can select which set of transponders it wants to tune at that moment. If you've got a couple of dual-tuner DVRs, that's quite a lot of coax. The latest little innovation from DirecTV is the SWM-8, which neatly solves this problem. It allows you to connect up to 8 tuners using as many splitters as you need (with the caveat that you need to have at least one branch of the splitters pass DC power from an indoor mounted power supply module). The way it works is very similar to SDV cable TV systems. There are 9 channels set aside - 8 of them provide one tuner's worth of signal down from the dish, and one is a shared upstream request channel from the tuners back to the SWM. Each tuner requests a channel to be allocated to it from the SWM at startup, and as the channels are changed, it requests a different satellite transponder be sent down its allocated SWM channel.

With this system, the satellite system itself can become arbitrarily complex, but the complexity can be hidden behind the SWM. Already the SWM can handle a single 5 LNB Ka/Ku dish plus two auxiliary dishes (one for international programming and one for carrying local channels for some markets).

As I've previously noted, this system is somewhat similar to SDV systems for cable - the only difference being that SDV channels are shared by all subscribers, not allocated solely to a single downstream tuner.

Verizon's FIOS offering already includes a box that transitions from fiber to coax for the household. In principle, that box could also provide addressable decryption so that the house simply sees all of the subscribed channels as clear QAM - no need for CableCard at all.

This same idea could apply in the world of cable TV as well. Each household would have an addressable box that would perform pre-tuning and decryption for a set of tuners within. There would be a spec for the channelization and for the upstream communication protocol. The channel data would be clear QAM. The same box could also have an Ethernet jack and provide IP service as well, for subscribers to cable-delivered Internet. Since the box obscures the cable infrastructure, it offers greater flexibility to the cable company in laying out their networks.